The invention relates to a recording and/or reproducing apparatus for a tape in a cassette which can be brought into an operating position in the apparatus where the tape is extracted from the cassette. The apparatus includes a tape-guide drum around which, over at least part of its circumferential surface, the tape can be wrapped along a helical path. A tape-guide device is movable between a first and a second operating position, for withdrawing the tape from the cassette and wrapping it around the tape-guide drum and for returning the tape into the cassette. A rotatable supporting ring surrounding the tape-guide drum carries at least two tape-guides which in the first operating position of the tape-guide device engage behind the tape inside the cassette. In the second operating position a first tape-guide keeps the tape wrapped around the tape-guide drum, a first portion of the record carrier extending from the cassette to said first tape-guide via the tape-guide drum and a second portion of the tape extending from said first tape-guide towards the cassette. A second tape-guide keeps the second portion of the tape away from the tape-guide drum, which second tape-guide is mounted on a pivotable lever which is loaded by a spring, which is arranged on the supporting ring and which comprises at least one positioning stop and at least one cam follower. The second tape-guide in one of the two operating positions of the tape-guide device is held in a first position relative to the supporting ring via the lever by means of an actuating-cam surface which cooperates with the cam follower on the lever. In the other one of the two operating positions the second tape-guide can be positioned in a second position relative to the supporting ring via the lever under the influence of the spring by means of a positioning stop which then cooperates with a counter-stop on the supporting ring.
Such an apparatus, which is intended for reproducing video and audio signals, is known from U.S. Pat. No. 3,821,805. In this known apparatus the second tape-guide is arranged on an L-shaped pivotable lever articulated to a one-arm lever which is pivotally mounted on the supporting ring, the two levers constituting a bellcrank-lever system. The L-shaped lever is loaded by a leg spring which acts against the one-arm lever and against the supporting ring. The free end portion of the L-shaped lever carries a pin which functions both as positioning stop and as cam follower. In the first operation position of the tape-guide device, i.e. in the threaded-out condition, said spring urges the pin into a substantially semi-circular recess in the supporting ring, which recess forms the counter stop, so that the second step-guide is positioned in its second position relative to the supporting ring defined by the positioning stop formed by the pin and the recess. In this second relative position the second tape-guide engages behind but is not in contact with the tape. When the tape-guide device is set from its first to its second operating position the pin is retained in the recess under the influence of the spring during a first stage of movement and the pin cooperates with an actuating cam surface during a second stage of movement, which cam surface moves the L-shaped lever against the force of the leg spring via the pin which functions as a cam follower, causing the second tape-guide, which is mounted on the lever, to be set from its second to its first position relative to the supporting ring, which first relative position is defined by the actuating cam surface. In the second operating position of the tape-guide device, i.e. in the threaded-in condition, the second tape-guide occupies its first relative position defined by the actuating-cam surface, in which position it is immobilized by the actuating-cam surface, so that also in the event of looping of tape and in the case that the tape exerts large tape-tension forces on the second tape guide this tape guide remains in its first relative position.
In such known apparatuses it is common practice to provide a search mode in order to enable a desired passage on the tape to be located rapidly, for which purpose the information signals recorded on the tape are scanned while the tape is moved with a high tape speed in the forward direction of the reverse direction between two rolls of tape which are each contained on a reel in the cassette. Searching for a desired passage necessitates search modes in the forward direction and in the reverse direction and, once a desired passage is reached, switching from the last search mode to the normal playback mode or to the stop mode. During switching the attendant change-over of the drive system for the record carrier and the dynamic behaviour of the tape rolls on each reel may give rise to undefined tape-tension conditions and hence to undesired loops in the tape. This is inevitable even if the tape drive system has a tape-tension-control device including tape-tension sensors, because during switching over of the drive system the operating conditions for such a tape-tension-control device are also indeterminate and the loops then occurring are so large that they cannot be detected by the tape-tension sensors of such a tape-tension-control device, which can perform only comparatively small displacements. When such loops are formed it is not unlikely that the tape slips off at least one of the tape-guide elements, which are then immobilized. Such elements include the tape-guide drum, the first and the second tape-guide of the tape-guide device and any further tape-guide elements and signal-transmission heads, so that when the tape is subsequently driven in the search mode it may be deformed and damaged.
Further, when in such known apparatuses the tape is returned into the cassette, i.e. during threading-out when one reel is braked and the other reel is driven to take up the portion of the tape outside the cassette, the instant at which the drive of the latter reel is started and the instant at which the drive of the supporting ring is started should be synchronised exactly. Should the drive of the reel start too early relative to the drive of the supporting ring this premature driving of the tape may give rise to very high tape-tension forces, which may lead to deformation and damage. Conversely, if the drive of the reel is started too late relative to the drive of the supporting ring, this may result in looping and in the tape slipping off at least one of the tape-guide elements, which during subsequent threading-out may lead to an incorrect operation and to deformation and damaging of the tape. As explained above, the risk of looping or the occurrence of excessive tape-tension forces, can neither be eliminated by a tape-tension-control device having a tape-tension sensor and operating during threading-out, due to the limited displacement range of the tape-tension sensor.